When I was a kid, we made traps like this sans yeast. I think we’d just leave 1-2″ of cola in the bottom of the bottle, cut and invert the top of the bottle, and set it out.
I recall having mild success with them with trapping flies.
Putting some rocks or something in the bottom might not hurt either…just to weigh down the bottle from blowing away.



http://www.diyhappy.com/quick-and-dirty-mosquito-trap/

Can't say that I ever went "fly trappin" ... but to each his own.

You don't do it for fun or sport...you do it so that you don't get eaten alive.

Oh ... I must have missed that part ... I grew up in the city ... We didn't have fun problems all like that ...